1. Field of Invention
The present invention relates to an assembly of an image pickup device, and more particularly to a zoom lens control mechanism.
2. Related Art
Image pickup devices, such as digital video cameras (DVC) and digital cameras (DC), have been widely used. One of the key elements of the image pickup devices is a zoom lens, and an object may be clearly focused on a charge coupled device (CCD) to be imaged by using the optical zoom of the zoom lens.
The zoom lens has multiple lens sets for a zooming purpose, and these lens sets may move relative to each other, so as to move from a focal distance position to another focal distance position. The moving stroke of the lens sets is determined by the optical design of the lenses. Generally, the moving stroke of the lens sets is mechanically controlled a cylindrical groove cam.
Referring to FIGS. 1A and 1B, a conventional zoom lens mechanical control mechanism is shown. The mechanical control mechanism has a lens barrel 110, six groove cams 112 and 114, lens 120 and 130, and a stepping motor 140. The lens barrel 110 is a barrel for holding the whole lens assembly, and is provided with two sets of groove cams 112 and 114 having the same curve and size in its periphery, each set of groove cams has three groove cams, so as to control the lenses 120 and 130 in a system, respectively. The lens barrel 110 has gear teeth 116 around the edge of its bottom, so as to be engaged with driving gears 142 of the stepping motor 140. When a zoom switch is turned on, the stepping motor 140 starts to rotate to drive the lens barrel 110 to rotate. The two lenses 120 and 130 move along the direction of the optical axis along with the movement of cam followers 122 and 132 disposed thereon with respect to the groove cams 112 and 114. Herein, the groove cams require a high accuracy, and are difficult to be manufacture with a high cost, and moreover, the groove cams are also quite difficult to be assembled and adjusted.
Referring to FIG. 2, another conventional zoom lens mechanical control mechanism is shown. The mechanical control mechanism has a first lens set 210 at a foremost position of a zoom lens assembly; a second lens set 220 adjacent to the first lens set 210 and disposed on a lens barrel 230; a threaded bearing 232, formed as a portion of the lens barrel 230; a positioning fork 234, formed on one side of the lens barrel 230 opposite to the threaded bearing 232; a stepping motor 240 having an outer threaded rod 242, which is screwed in a bearing hole of the threaded bearing 232 and engaged with the thread provided on the inner wall of the bearing hole; a third lens set 250, disposed on a lens barrel 260; a threaded bearing 262, formed as a portion of the lens barrel 260; a positioning fork 264, formed on one side of the lens barrel 260 opposite to the threaded bearing 262; and a stepping motor 270 having an outer threaded rod 272, which is screwed in a bearing hole of the threaded bearing 262 and engaged with the thread provided on the inner wall of the bearing hole. These components are all assembled to an assembly base 200. An image sensor 280 is further disposed on the assembly base 200, which is under the backmost element of the lens assembly.
Up to now, the conventional zoom lens mechanical control mechanism realizes zooming adjustment by moving the lens sets along the direction of the optical axis, so as to achieve zooming effect, with a result that the total length or the total size of a zoom lens module is unavoidably increased accordingly.